1. Field of the Invention
This invention relates to circular woven fabric extrusion coated with a polymeric film. In one aspect, the invention relates to circular woven intermediate bag containers having an interior or outer surface coated with a polymeric film.
2. Description of the Prior Art
Circular woven fabrics are used in a variety of applications, including intermediate bulk containers, explosive bags, and generic bags for a variety of commodities. The circular woven fabric offers the advantage over the more traditional linear fabrics in that there are no seams in the side walls. The circular woven fabric is normally manufactured in the form of a tubular body of the desired diameter. The tubular body is flattened and rolled onto a take up roll which is processed to form the bags. The bags may be formed by cutting longitudinal sections from the tubular body and either overlapping and sewing end portions together or stitching a bottom and top sections onto the tubular body forming an enclosed container.
The containers with circular woven tubular bodies, exhibit unusual strength and flexibility making them ideally suited for carrying large amounts of particulate materials and sometimes liquid materials. The intermediate bulk containers, for example, are commonly used to transport grains, minerals, polymer pellets, etc. The large diameters of such containers (e.g., from 40 to 60 inches) permit the transport of up to 3,500 pounds of material in a single container. The woven fabrics used in explosive bags are much smaller in diameter and are adapted to carry liquids.
In order to reduce or eliminate the leakage of material from the containers, it has become customary to coat the interior or exterior of the fabric with a polymeric film. One such technique involves extrusion coating the tubular fabric prior to its conversion into a bag or container. In this process, the roll stock of the woven flattened tubular body is first extrusion coated with a thin polymeric film on one side and then extrusion coated on the other side. In order to completely cover the fabric with the coating film, the extrusion coating extends a short distance, (e.g., in the order of one-half to one inch) beyond the lateral edges of the tubular body. The extrusion coatings thus are fused together in the form of a thin flap or seam extending outwardly on each side of the tubular body.
Although this process provides a complete coating on the tubular body, it has proven unsatisfactory because of the weakness in the fused flap or seam areas. The extrusion coating process inherently involves passing the coated fabric through the nip of counter rotating rolls which tends to compress the molten coating in the flap or seam areas to form thin sections. These thin sections present lines of weakness and points of failure, particularly failures resulting from high impact loads or with bag flexing during handling.